Polymeric iridium catalysts for C-H borylation of arenes under batch and continuous flow conditions.

Iridium-catalyzed direct C-H borylation of arenes has been extensively studied as an efficient method for synthesizing arylboronates. However, this transformation predominantly relies on homogeneous iridium catalysts, which are typically air-sensitive and difficult to recover. Here we show that pyridine-containing polymeric iridium catalysts can promote C-H borylation under both batch and continuous flow conditions. A ternary copolymer synthesized from 4-vinylpyridine, 4-tert-butylstyrene, and N-isopropylacrylamide served as an effective support for immobilizing and stabilizing the iridium species. This catalyst enabled batch C-H borylation of 20 arenes with yields up to 87%, as well as continuous flow synthesis of borylated products under ambient air conditions for over 24 h. XAFS analysis revealed partial reduction of the iridium precursor during catalyst preparation and in situ during the borylation reaction. This study provides an instructive and practical approach for designing immobilized iridium catalysts, thereby advancing the diverse applications of C-H borylation reactions.